1. Field of the Invention
The present invention relates to a redundant LAN system wherein an active and stand-by switching mode is adopted by a processing device, and to a method of switching between an active line and a stand-by line.
2. Description of the Related Art
In computer LAN network systems, to improve system reliability, redundancy is sometimes incorporated into the system, wherein the processing devices comprising the LAN system are provided with both an active line and stand-by lines in a redundant LAN architecture. In this redundant LAN system, when switching over from the active line to a stand-by line, it is necessary to provide task maintenance to maintain agreement of task status between different processing devices, that is to say, between the active line and the stand-by lines. This is because there is generally a one to one correspondence between LAN connections and tasks in the processing devices, and to maintain the LAN connection it is necessary to maintain the tasks in the processing devices.
However, with the switching method in the abovementioned conventional redundant LAN system, even though the task status is maintained before and after switching between the active line and a stand-by line, the hardware status among the LAN interface devices is not consistent. Consequently, this causes disagreement of the status between sub-LAN systems in the redundant LAN system, and there is a first problem in which it is sometimes necessary to break the communication connection with the other party""s communication device, and then re-establish the communication connection.
Furthermore, immediately after a line of the redundant LAN system is switched, an ARP cache table in each communication device on the same LAN segment as the redundant LAN, holds the MAC address of the LAN interface device on the previously active line of the redundant LAN system. Consequently, there is a second problem in that all communication devices on the same LAN segment transmit IP packets to the LAN interface device on the previously active line, and communication with the LAN interface device on the new active line cannot be performed immediately.
The present invention takes into consideration the situation mentioned above, with the object of providing; a redundant LAN system that maintains an equivalent communication connection to that immediately before switching a line, and enables the resumption of communication on a new active line immediately, a switching method between an active line and a stand-by line, and a recording medium.
In order to solve the above problems, a redundant LAN system according to the present invention is characterized in that with a redundant LAN system which includes sub-LAN systems with redundancy incorporated by an active and a stand-by mode, a plurality of the sub-LAN systems being connected to the same LAN segment, immediately after a sub-LAN system on an active line is switched, ARP packets for updating ARP cache tables of the redundant LAN system from MAC addresses of a previously active line to MAC addresses of a new active line, are transmitted from a sub-LAN system on the new active line to all communication devices connected to the same LAN segment as the sub-LAN system on the new active line.
Moreover, another redundant LAN system according to the present invention, is characterized in that with redundant LAN systems where a plurality thereof are connected to the same LAN segment, each redundant LAN system comprises: a plurality of sub-LAN systems comprising processing devices and LAN interface devices each given its own MAC address and connected to the LAN segment; and an inter-processor communication control device which connects the processing devices with a processor bus, and switches only one of the sub-LAN systems as an active line, the other sub-LAN systems being stand-by lines, and immediately after a sub-LAN system on an active line is switched, ARP packets for updating ARP cache tables of the redundant LAN system from MAC addresses of a previously active line to MAC addresses of a new active line, are transmitted from a sub-LAN system on the new active line to all communication devices connected to the same LAN segment as the sub-LAN system on the new active line.
Furthermore, a method of switching between an active line and a stand-by line according to the present invention is characterized in that with a method of switching between an active line and a stand-by line in a redundant LAN system which includes sub-LAN systems with redundancy incorporated by an active and stand-by mode, a plurality of the sub-LAN systems being connected to the same LAN segment, the switching method comprises: a step for starting an interruption processing program by a processing device in the redundant LAN system when a line switching event occurs; a step for stopping communication of a LAN interface device in the redundant LAN system; a step for dumping a hardware status of a LAN interface device on an active line to a memory in a processing device on the active line, in a situation where the communication is stopped; a step for deciding on a proper new active line by co-operation among the sub-LAN systems and an inter-processor communication control device; a step for copying a program execution status and the dumped memory status of the processing device on a previously active line to the new active line so that the new active line can resume a task from an interruption point of the previously active line; a step for resuming the task from the interruption point of the previously active line by the processing device on the new active line, based on a program execution status copied from the previously active line; a step for setting the LAN interface device on the new active line to resume in the same situation as the LAN interface device on the previously active line that performed the memory dumping; a step for resuming the LAN interface device on the new active line at a time when the resumption setting is completed normally in the LAN interface device on the new active line; and a step for transmitting ARP packets from the sub-LAN system on the new active line immediately after the sub-LAN system on the new active line resumes, notifying the MAC address of the LAN interface device on the new active line to all communication devices in the LAN segment, and updating the ARP entry for the redundant LAN system.
Furthermore, a recording medium according to the present invention is computer readable, and stores a program for a computer to perform this method of switching between an active line and a stand-by line.
Accordingly, with the present invention, in a situation where a communication connection has already been established with an other party""s communication device, when line switching takes place in the redundant LAN system, communication on the new active line is immediately resumed without breaking the communication connection with the other party""s communication device, maintaining an equivalent communication connection status to that on the previously active line before the line was switched.
That is to say, when switching from an active line to one of the stand-by lines in the redundant LAN system, a new active line takes over the task performance status of the previously active line, maintaining it as it was immediately before switching the line, and resumes from the point of interruption of the previously active line that was interrupted by the line switching. Furthermore, immediately after this line switching is complete, the new active line transmits ARP packets to all communication devices on the same LAN segment so that the ARP cache tables (association tables of MAC addresses to IP addresses of the redundant LAN system) are updated from the MAC address of the LAN interface device on the previously active line to the MAC address of the LAN interface device on the new active line.
In this manner, by combining line switching accompanying task status maintenance from an active line to one of the stand-by lines, with the updating of the ARP cache tables of the redundant LAN system residing in all communication devices of the same LAN segment, the present invention maintains the communication connection status between the new active line and the other party""s communication device, enabling communication to resume immediately.